Method for the digestion of materials containing cellulose



June 13, 1933. A. BROBECK 1,914,073

METHOD FOR THE DIGESTION OF MATERIALS CONTAINING CELLULOSE Filed Feb. 3,1932 3 Sheets-Sheet 1 B7: MW

A. BROBECK 1,914,073

METHOD FOR THE DIGESTION OF MATERIALS CONTAINING CELLULOSE June 13,1933.

Fild Feb. :5, 1952 3 Sheets-Sheet 2 Bmbeck veN 1W8 June 13, 1933, A.BROBEQK N 4 73 METHOD FOR THE DIGESTION OF MATERIALS CONTAININGCELLULOSE Filed Feb. 5,-1932 3 Sheets-Sheet 3 H- Ember/R Patented June13, 1933 UNITED STATES PATENT OFFICE ARNOLD IBBOBEOK, OF 38m GAVLE,SWEDEN mirnon ron THE monsrrou or IA'IEBIALS oon'rnn'me cnnLULo'saApplication filed February 8, 1932, Serial Elo. 590,871, and in SwedenFebruary 6, 1881.

The inventor has previously invented improved methods of producingcellulose by means of direct or indirect heating of the digestingliquor. by the circulation method.

As a result of these earlier inventions the important problem of theprevention of the formation of scale or incrustations on the heatingsurfaces has been satisfactorily solved, since the said earlierinventions have proved in practice that it is possible almost entirelyto avoid the formation of incrusta tions by passing the liquor throughthe heat ing apparatus with a relatively high speed along the heatinsurfaces. By using polished heating sur aces the speed of the liquor canto some extent be reduced.

However, further investigations have shown that considerableimprovements in the method of digesting may also be arrived at byimproving the conditions in the digester itself. Owing to the fact thatlittle attention has hitherto been given to these conditions the pulpproduced by the methods known up to the present has been uneven inseveral respects. This is primarily to be ascribed to the circumstancethat the conditions of temperature in the digester. have hitherto beenunfavourable as a result of which the degree of di estion of the ulp hasbeen different in di erent parts 0% the digester.

The investigations of the inventor have proved that the conditions whichare required for the production of as uniform 'a pulp as possible'arefirstly that the temperature within each horizontal zone of the digesteris practically uniform, and, secondly, that the average temperaturethroughout-the digestion is highest at the top of the boiler and fallssuccessively towards the base.

The investigations of the inventor have further proved that theconditions necessary for arriving at these results are, firstly, thatthe suction of thecirculating liquor from the digester is carried outuniformly either round the entire inner circumference of the digester orfrom points on the same which are equldistant from each other and,secondly, that the circulation of the liquor through the "digester,especially during the actual process f of digestion, takes place eitheruniformly upward from and down towards the strainer through which theliquor is removed or, if the strainer is located at some distance fronithe bottom, that circulation is effected both from above downwards andfrom below up: wards towards the strainer, the temperature of the li uorwhich is introduced below the strainer eing kept lower than thetemperature of that part of the liquor which is introduced higher up,the object of this being that suitable conditionsof temperature in thedigester should he arrived at.

It is also possible by means of the invention described above to makeimprovements when using systems of circulation in which regard has notbeen paid to the desirability of maintaining practically uniformtemperatures in the various horizontal zones.

The annexed drawings show two examples of a form of constructioncarrying out the invention described above.

Fig. 1 shows the digester with its preheater and pipelines, constructedaccording to the present invention.

Figs. 2, '3, 4 and 5 show details of the strainer on a larger scale.Fig. 6 shows a modified form of construction of the strainer and Figs. 7and 8 show details.

' The digester 21 is fitted at the lower end of its cylindrical partwith r a strainer 22, through which the liquor is sucked by the pump 24through the pipe 23 and is passed through the pipe 25, which goes outfrom the pressure side of the pump, to-the preheater 26, where it ispreferably heated indirectly. From thelatter, reheated liquoris carriedby the pipe 27 into the upper end of the digester.

Hitherto, the liquor which has eased the reheater, 26 has been introduceinto the ower end of the digester through the pipe indicated by a dottedline, as a result of which liquor of the same temperature has beenintroduced into both the upper and the lower end with the disadvantagesdescribed above.

According to the present invention that part of the liquor which is tobe introduced into the lower end of the digester is now taken from thepipe 25 on the pressure side of the pump through pipe 28 and is forcedthrough the latter into the lower end of the digester without havingpassed through the preheater 26. By leaving the pipes 23 and 28 Withoutinsulation the liquor is cooled to some extend while it passes throughthem, so that it is introduced into the lower end of the digester with asomewhat lower temperature than it has when it leaves the strainer.

As has been mentioned above the form of construction of the strainerthrough which the liquor is sucked out is of importance since it must beconstructed in such a manner that the liquor is sucked out as uniformlyas possible all the wayround the inner circumference of the digester.

The efi'ective straining area must be many times greater than the areaof the out-suck pipe in order that a sufficient quantity of liqnor canbe sucked out through the straining area when the fibres have been setfree when digestion has taken place for some time. WVith the forms ofstrainer which have been usedup to the present this relatively largeeffective straining area has had as a result that at the beginning ofthe digestion, before the woodchips have been broken up, suction hasonly occurred through the parts of the strainer nearest theout-suck'pipe and it is only when the fibres have been successively setfree that the suction has gradually extended to the entire strainingarea. V

By using the form of strainer which is the subject of this inventionthese disadvantages are eliminated by means of dividing the straineraggregate into a primary strainer provided with a large number of smallholes through which the liquor is sucked, and in con]unction with theprimary strainer and working together with it, a secondary strainerthrough which the liquor is sucked into an outlet channel, the secondarystrainer having a smaller number of comparatively large openings, thecombined area of which bears a certain proportion to the area ofcross-section of the out-suck pipe. This proportion should be so adaptedwith regard to the existing resistance to the flow that the liquor issucked out uniformly over the whole length of the strainer. In passing,it may be explained that if the area of the cross-section of theout-suck pipe be represented by 1,

then the combined area of the above-mentioned openings should amount tobetween 1 and 2. This means therefore that the total area of the holesin question must not be less than the area of the out-suck pipe andshould not be more than double the area of the outsuck pipe.

A suitable form of construction of the strainer is shown in the annexeddrawings in Figs. 2-5, of which Fig. 2 is a horizontal section of partof a pulp digester with its strainer. Fig. 3 shows on a larger scale across-section through the strainer along the line AB in Fig. 2. Fig. 4shows a longitudinal section along the line CD in Fig. 3. Fig. 5 showsthe same in perspective.

The steel-plate mantle of the digester is indicated by 1 and the liningby 2. The strainer which forms the object of the present invention isplaced round the inside of the digester lining and at the lower partthereof. The strainer consists of two parts X and Y in order to permitof expansion and contraction, the two parts joining on to the out-suckpipe Z. The strainer consists of two straining elements, an outer one 3,which is provided with a large number of small holes, and an inner one4, which is provided with a small number of larger openings 5. Accordingto the drawings the strainer elements are built up from a number ofstrainer plates provided with angle flanges, which run across thestrainer and are riveted to each other. The flanges on the plates in theupper strainer element are indicated by 6 and 7 and those in the lowerstrainer element by 8 and 9. A plate 10 is attached to the digesterlining and forms the bottom of the channel 11 in the ring-shapedstrainer. At one point in its length the channel joins on to theout-suck pipe Z.

The flanges 8 and 9 on the plates forming the inner strainer elementsupport the lower side of the outer strainer element 3 and divide thespace between the strainer elements into a number of separate spaces.The flanges serve further to give the strainer elements stability. Theflanges 6, 7 8, are however not essential and the plates may overlapeach other and be riveted together or they may be placed edge to edgewithout fastening.

When the circulating pump is working the liquor is first sucked inthrough the openings in the outer strainer element and enters the spaces13, from which it proceeds through the openings 5 into the channel 11and from there to the out-suck pipe. It is a suitable arrangement tomake the openings 5 of increasing size the farther they lie from theout-suck pipe, so that the largest openings are farthest from theout-suck pipe. In this manner the quantity of liquor sucked out througheach of the openings per unit of time will be practically the same inspite. of the varying pressures. By correctly adapting the areas of theopenings 5 in the inner strainer element with relation to each other andthe combined areas thereof with relation to the area of'cross-section ofthe out-suck With the form of construction just described the suckingout of the liquor takes place uniformly along the entire innercircumference of the digester. As has been indicated above, however, thesucking out need not necessarily take place along the entirecircumference but may also take place at a number of points thereonwhich are equidistant or practically equidistant from each other.

Fig. 6 shows arr example of a strainer in which the sucking out takesplace in the manner last described. The fi ure shows a horizontalsection of a pulp digester taken just above the strainer. The platemantle of the digester is indicated here also by 1 and the lining by 2.A pipe 30 is fitted round the inner circumference of the digester, theends of the pipe being at ca little distance from each other forpurposes of expansion and contraction. A number of perforated suctionpipes 31 are joined at regular intervals to the pipe 30 on both sides ofthe out-suck pipe 32 which leads from the pipe 30. The pipes 31 extenddown wards towards the bottom 33 of the digester along the taperinglower part of the same. The pipes 31 may either be all of the samelength or they may be alternately longer or shorter as is "shown bydotted lines.

Fig. 7 shows a vertical section of a part of the digester, illustratinghow the pipes 31 are fitted. Immediately below the junction between eachof the pipes 31 and the pipe 30 there is a flange 35 in which is fitteda disc 34. In this disc there is an opening 36 corresponding to theopenings 5 shown in Figs. 3 and 4. What has been said above regardingthe size of the openings 5 applies also to the openings 36, i. e. thatthe total area of the openings should be in the proportion [;:l to theareaof the out-suck pipe 32. In this second form of construction thediscs 34 thus form the above mentioned secondary straining elements.

Since the pipes 31 suck out the liquor from the whole of the lower partof the digester, it is not necessary with this form of constructiontointroduce liquor into the part of;

the digester below the straineras was indicated in Fig. 1 when astrainer according to Figs. 25 was used.

I lit is evident that the invention forming the object of thisapplicat'on is not restricted to the form of embodiment shown in thedrawings but thatthe elements may be modified in several ways withoutdeparting from the principle of the invention.

I claim: o 1. Method of digesting materials contaning cellulose withpositive circulation of the liquor through the'digester and through aheating apparatus and by sucking out the liquor through a strainer,located in the primary strainer element provided with a H great numberof relatively small perforations strainer elements provided with a smallnumber of relatively large openings distributed at equal distances fromone another, said openings communicating with a common chitnnel, and anout-suck tube from said channe on its surface and one or severalsecondary 3. Strainer for effecting a uniform suck- 3 ing out ofdigesting liquor from cellulose digesters, comprising a primary strainerelement provided with a greater number of relatively small perforations,a secondary strainer element provided with a small number of relativelylarge openings distributed at equal distances from one another, saidopenings communicating with a common channel, and an out-suck tube fromsaid channel, the relation between the sum of the areas of said openingsand the area ofthe cross section of the outlet tube being 1.

4. Strainer for effecting a uniform sucking out of liquor from cellulosedigesters, throu h which the liquor is circulated, consisting o aringshaped strainer body adapted to be fitted round the innercircumference of the cellulose digester, said strainer body comprisingin combination a primary strainer element having the form of a curvedplate body with a great number of small perforations and a secondarystrainer element consisting of a curved plate body with a relativelysmall number of equidistant larger openings, and located at. somedistance from the primary strainer element, a bottom plate so as to forma channel between said secondary strainer element and said bottom, anout-suck pipe communicating with said channel, a pump in said out-suckpipe, the relation between the sum of the areas of said openings in thesecondary strainer element and the area of cross section of the out-suckpipe being as 1.

5. Strainer as claimed in claim 4 characterized by the fact thatthespace between the primary and secondary strainer elements is dividedinto a number of compartments of substantially the same volume, eachcompartment communicating with the channel throu h one opening.

6. traineraccording to claim 4, characterized by the fact that theopenings in the secondary strainer elements are the larger the fartherthey are situated from the out-suck pipe.

In testimony whereof I have hereunto affixed my signature.

ARNOLD BROBEGK.

